Determining Environmental Drivers of Fine-Scale Variability in Blue Carbon Soil Stocks

Blue carbon ecosystems sequester and store a larger mass of organic carbon per unit area than many other vegetated ecosystems, with most being stored in the soil. Understanding the fine-scale drivers of variability in blue carbon soil stocks is important for supporting accurate carbon accounting and effective management of saltmarsh and mangrove habitats for carbon abatement. Here, we investigate the influence of local- and regional-scale environmental factors on soil organic carbon stocks using a case study from South Australia. We sampled 74 soil cores from mangrove, intertidal saltmarsh and supratidal saltmarsh sites where we also recorded precise elevation and vegetation data. Using a Bayesian mixed-effects regression approach, we modelled soil organic carbon stocks as a function of multiple environmental variables. The best model (Bayes R2 = 0.82) found that distance to the nearest tidal creek, vegetation type and soil texture significantly affected soil organic carbon stocks. Coarser soils with higher sand content had lower stocks, while finer-grained, clay-dominated soils had greater stocks. Mangroves had significantly greater stocks than intertidal saltmarshes and stocks were higher in sites closer to tidal creeks, highlighting the important role that local tidal creek systems play in sediment and water transport. This study’s findings are based on a broader range of local environmental factors than are usually considered in blue carbon models and increase our understanding and ability to predict site-level soil organic blue carbon stocks. The results emphasise the potential for organic carbon stocks to vary at local scales; the ability to predict this using appropriate environmental datasets; and the importance of accounting for local organic carbon stock variability when selecting sites for blue carbon-focussed restoration or conservation actions that aim to achieve carbon abatement.